UnderBreak
by azucaku
Summary: The monster and human relationship is more hostile, and the humans became the ones with the weaker souls. Because of this, however, humans became capable of magic in the same way as the monsters that now ruled over the surface. In Canada lives Sans and Papyrus, yet Sans isn't aware that his brother and his friends are hiding quite the load of secrets from him...
1. Chapter One: New Arrivals

_"_ _Heh... Of all the people to betray us, I never thought one of them would be you..."_

"Alright, it's decided then," Papyrus exclaimed while releasing a contained breath. "You two take the plans for now then." Undyne smirked and nodded, looking to Napstablook beside her as their eyes lit up.

"Where those papers are going, no one will ever get to them," they replied confidently.

"I'm trusting you two." As Undyne and Napstablook headed out the front door, one of the two upstairs began to creak. "Yes Sans, you can come downstairs now." the loud thumps that followed echoed in the near empty house as the skeleton ran down and hugged his brother.

"Yay yay yay!" Sans cheered, "We can finally hang out!" His eyes were filled with excitement like a child on Christmas morning, which prompted a soft laugh from Papyrus.

"Yeah, I'll take a break today, and I know exactly where we should go. But first... We have a house guest, and I'd like you to meet him before we leave." A tall, slender man walked out from the kitchen. He wore a black suit with an apricot colored turtleneck poking out of the top. Two noticeable cracks dug deep into his skull. One traced along his right eye up to the top of his head, and the other ran from his left eye to his mouth. "This is Doctor Gaster."

Sans blinked up at the man who he thought had to be at least twice his height. He gave Gaster a friendly smile before taking hold of Papyrus's hand and closing his eyes. Within seconds they were standing in a bright, grassy field that had no visible ending. Sans's smile grew even brighter at the sight, as he hadn't been outside their snowy hometown in Canada for a long time. He sat down in the green waves that caused him to seemingly blend in, pulling his brother with him before settling on his back.

"This place is really pretty brother," Sans commented with a contented sigh.

"Yeah, I'm glad. It wasn't long ago when there used to be a town here. The people vanished along with the buildings, leaving plants to grow in their places. No one really knows what happened to them all..."

Sans's expression was scrawled with excitement as ideas filled his mind. "Maybe they got to the Underground somehow? How cool would that be?!" Papyrus chuckled lightly and laid back.

"Still hoping to meet a human, huh?" Sans nodded slightly, and Papyrus shifted his arms behind his head as he admired the clear blue skies. "Me too bro, me too..."


	2. Chapter Two: The Fields

As Sans slowly awoke from his nap, he looked over to see Papyrus had fallen asleep as well. He lightly shook the taller skeleton awake.

"Hmm...? Oh, morning Sans..." Papyrus stood and stretched with a loud yawn. He remembered having needed to check on something after their visit to the fields, a soft sigh escaping him. "I have something important to take care of before we leave, alright? Don't go wandering off, I won't be long." With that Papyrus walked a few yards off, then vanished completely. Sans laid back on the grass chest down, his arms supporting his head and halfway hiding his face. He muttered to himself in boredom, and to his surprise a faint voice replied.

"Hey!"

"What the..." Sans looked around him, seeing that there were no visible monsters around him. Yet, the voice called out again. He was tempted to get up, but he stayed. "Papyrus said to stay here," he reminded himself.

"Hey, come on!"

"Who's there?" His green pupils became mere specks as a buttercup flower rose a few inches from his face.

"I'm Flowey!" it explained in a cheery voice, "Flowey the flower! Hee hee, you're so cute in this timeline, Sans!" his eyes lost color completely as he watched Flowey.

"W-what?!"

"Yeah! I've met a few of you before, but here... This you is so small! And innocent... _It'll be fun when I rip it out of you!_ And what would your brother think...?" The skeleton began to tremble and sweat as Flowey's face morphed and twitched during his speech. "Tell him and the scientist I say hi~!" Flowey then disappeared into the ground with a bout of hysterical laughter, leaving the distraught Sans by himself. A short while later Papyrus reappeared, a rolled up paper in his hand.

"Alright bro, you ready to head home?" he asked before noticing that his brother was shaking and crying. He kneeled down and wrapped his arms around him. "Hey Sans, shh... I'm here, what happened?"

"P...Papyrus..." Sans buried his face in his brother's shoulder as he began to calm down. "I-is it true...? Is there other... other "mes" out there?"

"Sans, where did you hear that?"

"A... A flower told me..."

"Shit," Papyrus muttered while picking up the smaller skeleton. Anger and panic were scrawled across his face while he held his brother close and vanished from the field. They appeared in Sans's room before Papyrus put him down on his bed and went downstairs.

 _Later_

"No Gaster! I'm not about to explain it all, alright! There are few things left here that I care about and I'm not letting your damn mess ruin what I have!"

"I hate it as much as you do," Gaster sighed. "I don't want anyone to ever know of the horrid things I've done, but leaving the young one in the dark will only cause us more problems. You know that. The only way we can keep him safe and know he's taking care is giving him the truth, so he can protect himself." Papyrus mumbled irritably under his breath, not wanting to admit Gaster was right. After all, if Sans didn't take it well it would only be an act at his expence.

"Sans," Papyrus called, "You can come downstairs now, okay?" The door to his room creaked open as the skeleton shuffled out, enveloped in a large mass of blankets. He made his way to the living room with painful slowness before seating himself on the couch. He was evidently still in shock over it all, though he'd calmed enough to stop shaking. Papyrus hesitantly cleared his throat, looked to the floor and began.


	3. Chapter Three: Gaster's Story

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 _The dark hallways stung with the scent of decay, which was so frequent that those passing through often didn't even notice. Loud, inhuman noises emitted from many barred off areas within the building and echoed into every otherwise quiet room. A tall figure passed though in silence as he carried a small package close to his chest. He soon reached a white door at the end of the hall, and his hand waved over the padlock. It opened immediately, and he hurriedly made his way inside before locking the door behind him. Along the walls were cupboards and cabinets that matched the door and walls, though some were stained with splotches of red._

 _"_ _Alright, calm down," he muttered to himself as he shakily opened the box. Inside were two carefully wrapped needles, each containing an odd red liquid. He placed the box on a nearby table, which other than a small potted flower had been clear. It was slightly hunched over from the lack of sunlight, and seemed to stand up as it was injected with the contents of one of the needles._

 _"_ _Gaster," Alphys mumbled shakily as the door swung open. She quickly stepped in and closed it, and despite the look of relief that met Gaster he was still notably overwhelmed with nervous tension._

 _"_ _You're just in time Alphys," he said in reply, "I figure it'd be safer with you around. I'm sure you heard of my... passed test subjects... but I'm changing it all. I'm sick of hurting all these innocent people in an attempt to free others..." Alphys gave him a weird look as he took out the other needle._

 _"_ _What is that stuff? What exactly have you been doing in here?"_

 _"_ _It's determination, Alphys. If monsters can obtain the humans' trait, we could gain even more power. Perhaps, even enough to break the barrier once and for all..."_

 _"_ _W-what?! Gaster, they'll kill you if they find out! You know that!" Her brow furrowed in concern._

 _"_ _I don't care what they will do. Alphys, dear... You are still young. You have much more left for you, more to have put on the line for a risk like this. I'm getting old. All I have left is my research."_

 _"_ _Gaster, I-"_

 _"_ _I beg you, keep this between us... You'll have to forgive me for this," he muttered softly as he raised his shirt, stabbing the second needle into his own soul. Alphys's eyes went wide in shock as the doctor dropped to his hands and knees, groaning in pain. She reached forward to help him up, recoiling suddenly when he let out a low growl in reply. His hands grabbed the edge of the table, seemingly melting onto it as he attempted to stand. Yet, after a few moments, he managed to settle and reform himself properly. Alphys stared at him with wide eyes as she trembled before running out of the lab. Gaster meekly let out a sigh and closed his eyes, laying himself there on the floor to think._

 _While the first few DT experiments had been easy enough to recover from, Gaster's physical state began to wear down each time. Within three months the damage was more than apparent. Cracks had formed in his skull, his right eye sat in a permanent half-closed state, and large holes had formed in the palms of his hands. Even so, he continued to push his limits. After all, he had been the first to survive his own testing. He wasn't prepared to end them just yet._

 _Gaster had begun traveling to the Underground at the few times Toriel wasn't keeping watch over the barrier. At first the humans attacked him in fear, but over time they saw his lack of will to fight and accepted his presence with relative peace. While his research continued to improve from all of this, it didn't come without consequence. Alphys received great amounts of stress as she desperately covered for him, and even the slightest mess up from either of them would cost Gaster his life._


	4. Chapter Four: Please Brother?

"So you ended up here to get away from the King and Queen?" Sans asked as he slowly processed everything he'd been told. Gaster nodded in reply to the question, and the small skeleton's face suddenly lit up like fireworks. "Wait... So you've been to the Underground?! What do humans look like? Were they really strong? Did... did you ever have to fight a human?"

"Bro, calm down," Papyrus replied with a slightly relieved laugh. "Yes, he's been to the Underground several times."

"I want to go there!" Sans cheered, pulling the blanket from over his head. Gaster smiled and set down his mug as he felt Papyrus glaring daggers at him suddenly. "Is there a way we can go Mister Gaster? Please?"

"Absolutely not," Papyrus growled.

"Papyrus, I want to do this for the child. Alphys... Perhaps she will help. After all, she never told the king of my treason. At least, not in this time..." Sans looked down in disappointment, though it was evident he only understood half of the conversation. Papyrus let out a soft sigh.

"Fine, we can go to the lab and get your supplies. I'll call Undyne and-"

"But brother, I want to come with!"

"No! You are going to stay here where it is safe!"

"But Papyrus-"

"'But' nothing! The lab is very dangerous and I won't risk you!" Sans's eyelights dimmed and shifted away from his brother. This was the first time he'd been yelled at. Even when he'd traveled to the castle alone or went out after dark to play in the snow, Papyrus was never much more than a bit stern. He noticed this and felt his heart drop out of his chest.

"S...S-Sans, I... I'm so sorry," he mumbled out, breaking the silence that came over the three. "You don't understand the dangers we've put ourselves into, little bro... You're the only purity left in my life. Gaster, Undyne, Napstablook... All of us could be hauled away and killed for what we've done. I can't... I won't let you follow in my footsteps."

"But brother, I'm stronger now," Sans replied with a glimmer of hope. His eyelights were almost impossible to see as tears streamed down his cheekbones. "I might be smaller than you all but I can handle it! Even if my HP is low..." He winced as he brought up the fatal flaw. "I want to prove it Papyrus... I want to be helpful."

"Give him a chance," Gaster added. "We can test him first and make sure he's ready. Then we can go to the lab, and if anything goes wrong you can bring him home." Papyrus let out a slight groan.

"Fine, fine. I'll give it a chance." Sans jumped up excitedly and hugged the tall skeleton tightly. He smiled and hugged back. "We'll do some training tonight and test you tomorrow morning before we leave."

"Thank you thank you thank you! I won't let you down brother, I promise!"

"I know Sans, I know."


End file.
